Electrolytic deposition of cadmium



C. G. HARFCRD ELECTROLYTI@ DEPOSITION CADMIUM www/aorigina'l Filed July s, 1937 Muga/15? P .sf /2 /a /4 /f/J/P /a im A ful/1 N4;

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l Patented May 29, 1945 UNITED STATES PATENT oFl-lca amazes ELEo'noLmc omsloten on ommen Charles G.. Harford, Quincy, Mass., ox' to Arthur lli. Little, lne., dlamlsriclse, Mess., a oor poration. of Massachusetts originel application ons c, les?, sensi No. lgd, now Patent No. tl), August d, Miedo molded and this application Novemher it, i943, Serial No.. lhlll A c claims. loi. cosmesi' This invention relates to an improved method of electrolysis, including the electro-deposition of metals, particularly cadmium, and to the composition of the electrolyte. This application is a continuationl-part ci application Serial No.

21,809, led May 16, 1935, and a division of ooadopted and adhered to,`in spite of the wellknown intensely poisonous character ofcyanides and cyanidesolutions andthe danger which is consequently incurred throughout the plants in oi reagents and of electric ctn-rent, accordingly, are objects of the invention. Other ololects will t appear from the following; disclosure. i

i sallentileature of the present invention is the discovery that cadmium is subject to a inlilorln electrolysis and undergoes e, dependable dissolu-z tion. and regular deposition ol the instal' under the lll innuence of an electric sortent, ll the electr clyte is of substantially ccmposition'hetween the anode and the cathode and contains a hydrocartoon poiyamine such as ethylene diamine It may he further enhanced il an excess ot 'the hydrocaruon polyamine is present., The informeer `oon polyarnine added, .whether in excess or not, does not appear to loe permanently alleeted by the electrolysis and even after prolonged use of the .bath it is found upon analysis to until` minished its total content.

The hydrocarbon polyaniiue combines with. thel metal or with .the cation of the electrolyte and 1:articularlyA with the `metal component of the which such compounds must be stored, handled, operated with and replenished from time to time.

Other procedures have been followed, it is true, but these, in general, entail the use of two or more solutions operating as a batch process. Qperating in this way it is necessary to add chemicals to certain parts of the system and to withdraw and discard worthless by-products from others0 ln thus destroying or converting the components of the electrolyte tosome other form, these processes of the prior art involve the unnecessary and hence salt, to :form therewith a comples ion which is readily susceptible to ionization, electrolytic transfer tothe cathode, and discharge oi the metal ion and deposition ci the metal in solid form thereon The metal content oi' electrolyte is replenished hy the direct corrosion and dissolution ofthe anode.

Ey the expression electrolytie deposition as used in the present application end in the claims,

` ls to be understood the electrolysis of an electrolyte, contalrninsl one or 'more metals in solution,

, and forming a continuous liquid medium between wasteful consumption of reagents and of electric current or energy, as well. l

It is accordingly an object of this invention to provide an improved method of electro-deposition in which satisfactory or improved results may be.

accomplished and in which compounds other than the cyanides, and which are essentially non-poisonous, may be used.

Another object is to provide a method in which the current eineiency may be improved., A further Objectis to lobtain a brighter plate. f,

Itis also an object to provide an electrolytic process and an electrolytic medium wherein the reaction consists ln eilecting electrolytic transfer 4 of the metal (anode) to metal (cathode) without side reactions or at least without side reactions resulting in the cumulative formation of ancillary lay-products. and in which the only cumulative the catlode and a soluble metalvanode, winch lncludes the separation and deposition of said dissolved metal or metals upon the cathode, and

simultaneously dissolving or the metal anode,

thereby replenishins and maintainingthe metal content of the electrolyte.

The anodes, formed of cadmium, are uniformly and' regularly dissolved into the electrolyte without disili-tacere.tionV and the resulting formation o! residual granules or powder..

product is that-of the electrolytically deposited metall on the cathode, and in which the only required addition is that of replenlshingrauch metal in the system, as a metal at the anode. Economy The process is characterized'hy being applicable to metals which are able to form complex cations containing a hydrocarbon polyarnli'lec The proof that such complex ions are formed ls that the metals in the form of the cornplex ion can exist in alkaline solution whereas the corresponding simple metal ions are -precipitated when made alkaline, as by the hydroxide of anV alkaline metal.

Hydrocarbon polyamines contain carbon, ni-

;trogen. and hydrogen and .no other elements.

They are thus distinguished troni ammonia, and -also from the alkylolamlnes which containoxy- 'Ihe general formula of hydrocarbon polyamines suitable for use in connection with this process is therefore:

Hari-(CH2) n-NHR where n is 2 or more and R is hydrogen or the radical (Gl-Iz) n--bI-IR R. being the same as just explained.

The process cf the invention, as described in the above-mentioned applications, may be carried out, for example, with salts of certain monoyvalent metals, such as silver, with salts of I bivalent metals, such as copper, cadmium, zinc, and nickel, with salts of trivalent metals, such as iron and chromium, and salts of tetravalent or hexavalent metals, such as platinum and tungsten, in the presence of the polyamine. In these metallic polyamine complexes, the polyamine and the metal are attached to each other by the secondary valences of the 'nitrogen and of the metallic atoms. Since only secondary valences are involved,

not alter the change or 'valence of the cation.

'I'he metals with which the invention may be carried out as described in the above mentioned applications are indicated in the chart of Fig. 1, in which the symbols of the elements are shown in the order of their atomic numbers, arranged in accordance with the periodic table. The metals with whichthe present invention, as described in the above-mentioned applications, is applicable are enclosed by the dotted line.

Fig. 2 is a more or less diagrammatic illustration of the type of electrolytic cell and indicative of the type of electrolysis with which the process may bev practiced, namely, one in which the electrolyte is continuous from electrode to electrode.

In practice, it is now found that when cadmium is made the anode, with respect to an electrically conductive cathode, and an aqueousfluidfelectrolyte is provided, extending from the surface of one to the surface of the other lWithout interrupas above dened, the application of' an electrical potential or current between the electrodes willresult in the dissolution of the anode and the electrolytic deposition of the metal upon the cathode, withoutv side reactions and without change of regulation other than the addition of metal as metal 'the entrance of the polyamine into the cation does v lbe present 'to advantage,l especially where it is economical to employ.

In either case, however, it is essential that the fluid medium of the electrolyte between the anode and cathode be unobstructed, continuous, and preferably uniform, as by agitation.

In Fig. 2 it will be observed that the electrolytic solution l is contained in a single vessel 2, which is preferably lined with rubber, and forms a continuous medium between the anode or anodes 3- (which are connected to the positive bus barsy il, and are composed of.. the metal or metals to be deposited) and the cathode or cathodes 5, which are connected to the negative bus bar E, and upon which the metal is to be deposited. The uniformity of the electrolytic solution during operation may be promoted by agitating the electrolyte with any suitable means (not shown) but is substantially automatically preserved throughout the reaction which is accurately represented, in its net effective result, by the equation Metal (anode) Metal (cathode) for there is no cumulative consumption or conversion of the other constituents of the electrolyte into by-products and hence no necessity for replacement or reconversion, even upon long and y continuous operation.

It is found that hydrocarbon polyamines react with ionized salts of cadmium, in aqueous solution, to form various orders of compounds'. The

number of compounds so .formed varies, in accordance with the number of secondary valences (as set forth in theories of Werner complexes),

but need not be gone into here in any great detail asthe invention will be clear from the disclosure herein.

It is generally preferable to use at least 2 mols of hydrocarbon polyamine to one mol of th salt of cadmium, and best results range between about 21/2 and 6 mols of the polyamine to one of the salt. More polyamine may be used, but there is no particular advantage in so doing.

tion, containing a soluble hydrocarbon diamine Typical and representative examples of the practical application of this invention will-now be described in its relation to electroplating, with respect to cadmium and to various salts of the varily available in the form of a 40% or 60% solu-l tion in water.

In carrying out the process of this invention, the temperature of the bath is preferably at, or somewhat above, room temperature, generally between 25-C. and 40 C.

' 'I he electrolyte I may be contained in any suitable resistant vessel 2 which is preferably a nonconductor of the electric current, such as earthenware or rubber. The anodeA 3 (or anodes) may conveniently consist of cadmium strips which are connected to a'source of` electric current and are suspended in the solution, preferably so as to be completely submerged, as by bus-bars 4, having a chemically resistant or protected conductor. The cathodes were connected to a suitable source of electric current to provide a current density -of 20 to 40 amperes per square foot`of cathode .ceelmilzkm eelt:

3 @Ealmlzo ...,grems-- llllll .Ethylefle diamine ..-clo lo@ Sellerie eclm--- To eleve pH oi? lo Weiler A To make 1000 c. c.

The plating is carried out by the procedure alreecly described, using about room temperature or slightly above, say 25 to 40 C. .A metallic oeelmlem anode is used, and goed results efe oletelnee with currenlJ density of about 2o empezes per selxexe fool; of the cathode. Bresssteel or other euieble metal is used es the cathode.,

The working range of the ratio of Iethylene lill- Y eemeee The opere-tion of elle feecton is smootli emi com timioue Terms e erlebt, uniform deposit el metal on elle oellloele emol prolonged for sobsteotlellgf eey desired period of time without came ,emilie lo eelt 'ls between 2 and velzmisll. l0 of the l tween 9 and 10.3. -Lower values give e spomgy Y plete; with higher velues there is poor adherence emol little meting.

It possible to use more then one sell; of the seme metal in the plating beth, il desired;

procese. For exemple, brass may oe successfully oletecl by using bress modes and a. befall of copper encl'eliio selle'. v

.es @escriben in the above-mentioned applica wens., il. is possible lio carry eut elle process ci `this invemeiom Without fliet dissolving" a. salt of the mem! to lee plated in che beth. In such ceses, the motel of` the anode dissolves lo furnish sum- Such procedure has no particular edor @they ellen elle simply of em eleeizi'lo current, emi eeplenelnmeml; of the 'metaal of the mamies, emol femme?. replacement of "elle pletecl eellioee, leem aime to time, if enel when leslie-1L lli @here le teelenoy for loe-cio sells of the eleoirolyize lo seeemle, es for exemple., el; ehe cathode (with solutions oomelmne e lowes milo of hydrocexoon polyemme oo metallic sali; einen 2:11). which might loiteiefe wien elle oomleeioy of the eleposlion er of the elated suece comme, this may l.ce evereome by elle addition of sommo eem (in o elillefle. sells or ooreespomelimg acid im ceee of oline? selle) or of elle mlyomlne, or bolli., lele-miem of elle or of elle eotlioe is likewise helpful.

1. le eeeeoes for' elle elecoolytic demolition of ceclmil'ee, olnemecterieeel ley consistjine essentially of solelsle'sell'. of cadmium enel en relleyl laymlroeemom eelyemlree eno memliesb me e pH velue bel-Ween eoproxlmetely 9 .and ill. 2. .im eeoeoos eleetolyee for the eleceeolyolc y I; elemelelom of oedmimma. eheieoteeieeol ley comlstn It: le else possible to plete alloys by the present me essenlsiolly of e eoleole sel@ o ceclmlum end eeleyleiee @lemme eee meeiesolne e pH velue oet-Ween epiemximelely 9 emi lose.

3. A process of eleceelgrele met comprises elec tiiomclepcsitlmg cadmium from en undivided oell vantage when plating with most ordinary metals,

lout when the reifer metals ere used, such es lame- Vsteel emol platinum, emlmetals of 'the platinum groups, it is generally inconvenient and exoemslveV to use their salts in the loath, and adequate resulla con be obtained es far as such metals are concerned when an anode of the metal to be plated is placed in a bath containing 'a hydrocerbon polyomlne and the plating carried out' as clescrlleed above. For instance, e tungsten anode is immersed-in a bath containing 25% ethylene diemiixe in water. Y u

Flellnum. and other metals of lthe platinum group may be plated ln the same wey.l Alternatively, l! desired, salts of these metals may be added to the plating baths and the procedures of the preceding examples may be used.

coeeoinime en aqueous eleeiolyl;e consisting eseemlslelly of soleilile of cadmium amel en elim llycleoeereon oely.. eine .emol memfesemg e. @live-lue leetweeneemoximeoely e like,

4. A precees of eleeeeolysle that cemorises electroucleooellzmg ceclmiem from en undivided oeil oonieiiliee mi eeueeeeelecei'olyte consisting eseeiillelly of e soluble sell; of cadmium and ethylene cliemlme emi menliestlee e. pi value between n e o., Heeroma. 

